"They do this every night. They come in every night," said Michael Bartlett of Mills Music.

And they seem to just keep coming.

There has to be some scientific explanation for this phenomenon.

The crows are headed to the wetlands on the University of Washington's Bothell campus - their roost.

For one of the world's foremost crow experts, Dr. John Marzloff, this just never gets old.

They come in waves, swirling black clouds, clans of crows from all corners.

"Over the last three to five years, they've gradually coalesced here to this wetlands area and now it seems like the birds are coming from Seattle, Sultan and other places up the Skykomish Valley and they're all coming to this one spot," said Marzloff.

Marzluff's official estimate is 10,000 birds - a nightly slumber party that finally grow quiet as they take over the wetland for the night.

Marzloff believes the crows find power and safety in numbers and this is a centralized location where they can all meet - for who knows what.